This invention relates to solid propellant compositions and to a novel family of energetic liquid plasticizers for use therewith. In a more specific aspect, this invention concerns itself with the use of a novel family of azidonitrocarbamates as energetic plasticizers for advanced solid propellant compositions. In still another specific aspect, this invention concerns itself with the use of azidonitrocarbamates as a means of reducing or minimizing the amount of smoke in the exhaust gases generated during the propulsion phase of solid propellants.
The increased utilization of rockets and missiles has spawned a considerable research effort in an attempt to improve the performance characteristics of solid propellent compositions. Generally, solid propellants consist of one or more organic or inorganic oxidizers dispersed in a resinous binder matrix which may also function as a fuel. Typical oxidizers are ammonium perchlorate or HMX (cyclotetramethylene tetranitramine) which are well known in the art. Various resinous components, such as hydrocarbons, polyesters, polyurethanes and other like materials may serve as the binder/fuel matrix. A supplemental fuel component, such as finely powered aluminum, may be used also. Other additive components, such as anti-oxidants, burning rate modifiers, wetting agents, anti-foaming agents and plasticizers may be added to the propellant composition, if desired. Dibutylphthalate or triacetin are generally employed as inert plasticizers in combination with the resinous binder material.
In using solid propellants, however, a problem exists in that an undesirable amount of smoke is often produced in the exhaust gases emanating from the solid rocket motor during propulsion. Excessive amounts of smoke are extremely undesirable in the exhaust gases since this provides data which pinpoints the sites from which the missiles or rockets are being fired. During previous efforts at overcoming the problem of excessive smoke, it was suggested that HMX be utilized as the oxidizer component since ammonium perchlorate liberates hydrochloric acid as a primary exhaust product. The acid is a strong smoke producer. Although the use of HMX as an oxidizer tended to reduce the amount of smoke produced in the exhaust gases, its use did not sufficiently overcome the problem and telltale amounts of smoke were still produced.
As a consequence, a continuing research effort was maintained since there still existed a need for a solid propellant with a minimum amount of smoke in its exhaust gases coupled with performance characteristics as good or better than solid propellants that have excessive amounts of smoke in their exhaust gases. In furthering the research effort referred to above, it was unexpectedly discovered that a new family of azidonitrocarbamates could be employed as energetic plasticizers in the fabrication of an energetic smokeless propellant. The novel plasticizers of this invention replace the conventional triacetin inert plasticizer generally utilized in conventional HMX composite propellants. The resulting propellant not only produces a minimum amount of smoke during propulsion but, also, shows a significant and unexpected improvement in specific impulse characteristics.